Process and apparatus for astigmatic and spherical subjective testing of the eye

ABSTRACT

An apparatus and process for determining subjective astigmatic and spherical prescription for the eye is disclosed. A target, consisting of a straight line, is focused for maximum clarity by the adjustment of spherical optics, causing the line to become proximate to the retinal viewing plane of the eye. Change of astigmatic correction is made along at least one axis diagonal to the line until maximum sharpness of the line results, without resultant spherical change and resultant movement of the image away from the retinal plane of the eye being tested. A second target, again consisting of a straight line, is introduced; this line target is angularly inclined to the first target, preferably at 45°. Spherical adjustment is made to obtain subjective line sharpness. Change of astigmatic correction is made along at least one axis diagonal to the line until maximum sharpness of the line results, without resultant spherical change and resultant movement of the image away from the retinal plane of the eye. By the expedient of vector analysis of the two astigmatic components, astigmatic correction can either be plotted on Cartesian coordinates (in accordance with a technique recently developed), or conversion to the more conventional polar description of astigmatism using cylinder power and rotation can occur. A specialized line target consisting of a three point source smeared by the superimposition of strong cylinder in the range of 4 to 12 diopters is disclosed. This specialized target, when the point sources are arrayed in a triangular configuration, can be adjusted using patient Vernier visual acuity, a visual acuity common to a high degree in large numbers of the population.

FIELD OF THE INVENTION

This invention relates to subjective eye testing apparatus fordetermining astigmatism and spherical correction.

SUMMARY OF THE PRIOR ART

Subjective measurement of astigmatism has heretofore related to patientfocus on a radial array of spoke-like lines. Best spherical lenscorrection is determined. Additional positive sphere is added. The spokeline appearing sharpest is the one nearest one of the requiredastigmatism axes. Negative cylinder can be added at 90° to theorientation of the sharper line until all lines are of similarsharpness. The process may be repeated with variations known to thoseskilled in the art. Finally, when the astigmatic correction reachessufficient precision, other optimizing techniques such as the employmentof a Jackson crossed cylinder may be introduced.

These prior art techniques have several disadvantages. First, thepatient must be sufficiently instructed by the eye examiner to look forthe spoke or other linear target having the optimum visual appearance.The process of instructing the patient ang getting the patient tounderstand the instructions is time consuming and to portions of thepopulation extremely difficult. This is because of the presence ofvisual aberrations, lack of visual coordination, or absence of basicintelligence and experience (as, for example, in the case of youngchildren).

Additionally error, especially at low diopter cylinder power, can occur.

Finally, the patient is inhibited in responding to such conventionaltests by his own expected predelections to size and shape. Adjustment insphere produces resultant change in size; the patient, not accustomed toresultant change in size, confuses desired optical clarity withpreventing undesired size change. Erroneous spherical prescription canresult.

Similarly, adjustments in cylinder produce resultant change in targetgeometry; the patient, not accustomed to resultant change in targetgeometry, confuses desired optical clarity with preventing undesiredtarget geometry change. Erroneous cylindrical prescriptions can result.

BRIEF DESCRIPTION OF THE INVENTION

An apparatus and process for determining subjective astigmatic andspherical prescription for the eye is disclosed. A target, consisting ofa straight line, is focused for maximum clarity by the adjustment ofspherical optics, causing the line to become proximate to the retinalviewing plane of the eye. Change of astigmatic correction is made alongat least one axis diagonal to the line until maximum sharpness of theline results, without resultant spherical change and resultant movementof the image away from the retinal plane of the eye being tested. Asecond target, again consisting of a straight line, is introduced. Thisline target is angularly inclined to the first target, preferably at45°. Spherical adjustment is made to obtain subjective line sharpness.Change of astigmatic correction is made along at least one axis diagonalto the line until maximum sharpness of the line results, withoutresultant spherical change and resultant movement of the image away fromthe retinal plane of the eye. By the expedient of vector analysis of thetwo astigmatic components, astigmatic correction can either be plottedon Cartesian coordinates (in accordance with a technique recentlydeveloped), or conversion to the more conventional polar description ofastigmatism using cylinder power and rotation can occur.

It has been shown that measurement of astigmatism can be determined andplotted at two components 45° one with respect to another. By plottingsuch components on a 360° chart, rotation and power of cylinder(especially low power cylinder) can easily be determined. See patentapplication Ser. No. 263,329, filed June 15, 1972, entitled"Ophthalmological Apparatus and Process Having Independent Astigmaticand Spherical Inputs", now William E. Humphrey, U.S. Pat. No. 3,822,932.

A specialized multi-line target created by 4 to 12 diopter cylindersmear consists of point sources disposed at the three apexes of atriangle. By utilizing the cylinder to smear the point sources normal tothe base of the triangle and measuring astigmatism along at least onediagonal component of measurement inclined with respect to the axis ofthe smearing cylinder, an array of three lines is generated. Sinceastigmatic viewing, when corrected along one component of astigmaticmeasurement, results in all three smeared lines being equidistant onefrom another, an astigmatic test results which enables the patient toequidistantly space a central smeared line from the remaining smearedlines. The ability to center or align line segments, commonly known asVernier visual acuity, is possessed by large samples of the population.

FURTHER OBJECTS AND ADVANTAGES OF THIS INVENTION

An object of this invention is to disclose a process and apparatus fordetermining astigmatism and spherical prescription with each measurementbeing determined in isolated components.

An advantage of determining astigmatism in two isolated components inaccordance with the apparatus and process of this invention is that theadjustment of one component of astigmatism does not affect theadjustment of the remaining component of astigmatism.

A further advantage of the apparatus and process of this invention isthat adjustment of the spherical input is independent of both of theastigmatic components of this invention. Change of the sphericalprescription does not require correspondent change in either of thedetermined astigmatic prescriptions.

It should be noted that the spherical prescription is completelydetermined at an unexpected place in this test. Immediately before thedetermination of the second astigmatic component, spherical prescriptionis determined. Thus, the unexpected sequence of prescription of thistest is first to determine one astigmatic component of correction for apatient's eye; second, to determine the total spherical componentnecessary for correction of the patient's eye; and finally, to determinethe remaining astigmatic component for correction of a patient's eye.

It should be further noted that each line target requires adjustment ofonly two, and not three optical components. Each line target requiresadjustment of the spherical component, and that astigmatism componentwhich varies astigmatism diagonally to the orientation of the straightline target. Adjustment of that astigmatism component which variesastigmatism parallel and perpendicularly to the orientation of thestraight line target is not made.

An advantage of each straight line target is that it requires adjustmentonly to its correspondent variable astigmatism component and thevariable spherical component. Surprisingly, these adjustments can bemade in any order.

A further object of this invention is to vastly simplify the instructionto the patient. The patient is only told to optimize the view of astraight line using discrete spherical and astigmatic controls. Room forconfusion with other imaging phenomena, such as changes in shape andsize, is completely eliminated.

A further advantage of this invention is not only the product of vastlysimplified instructions to the patient, but additionally the product ofthe discrete and independent shperical and astigmatic adjustments.Adjustment of any one of the three optic inputs (one spherical input andtwo astigmatic inputs) is completely independent of the remainingoptical adjustments. No interrelated adjustment is required.

A further object of this invention is to disclose simplified straightline targets for viewing by the patient, the target always consisting ofat least one straight line.

An advantage of using a straight line target is that with sphericalpower change, no disturbing magnification change occurs to the patient.The patient can change his acuity with respect to a straight linewithout disturbing size changes which tend to inhibit his subjectiveresponse to the optical test.

A further advantage of the straight line target used with this inventionis that with astigmatic corrections, no disturbing shapes changes occurto the patient. In viewing a straight line, the patient sees anunchanging target save and except for the optical clarity with which thetarget is seen.

An object of this apparatus and process is to provide an instrument withan image which is coherent to measure astigmatism in two separatecomponents only.

An advantage of the image produced is that while astigmatism in onecomponent is measured, astigmatism error in the remaining astigmatismcomponent is completely obscured. The image, being only sensitive to onecomponent of astigmatism, can determine that component of astigmatismwith a high degree of accuracy, and with a minimum of confusion, as thetest is specific to a particular type of astigmatism component.

A further advantage of measuring astigmatism in separate components isthat a plot of the components to determine ultimate astigmaticprescription in cylinder power and rotation can be made with greaterease and higher degrees of accuracy than is now conventional.

Yet another advantage of the apparatus and process of this invention isthat it can easily be constructed in the form of a hand-held instrument,or alternately easily inserted in and used with existing optical testingequipment.

Yet another object of a specialized cylinder smeared line target of thisinvention is to couple the measurement of astigmatism to patient Verniervisual acuity.

An advantage of utilizing patient Vernier visual acuity for subjectivemeasurements of astigmatism is that high degrees of Vernier visualacuity are possessed by large segments of the population, and that linecentering possesses information as to which direction additionalincrements of adjustment must be made.

DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of this invention can be morefully understood, reference being had to the following specification andattached drawings in which:

FIG. 1 is a schematic perspective view of the eye test device of thisinvention, schematically illustrating a target, a patient's eye viewingthe target, and thee corrective optics intermediate the target and thepatient's eye, and a schematic representation in planar form of theretinal plane of the patient's eye;

FIG. 2 is a view similar to FIG. 1 illustrating the first sphericalpower adjustment of this invention;

FIG. 3 is a view similar to FIG. 1 illustrating the determination of thefirst component of astigmatic correction of this invention;

FIG. 4 is a view similar to FIG. 1 illustrating an angularly inclined(preferably at 45°) new target with the second and final sphericalprescription change being made to determine the spherical prescriptionrequired for the patient;

FIG. 5 is a view similar to FIG. 4 illustrating the determination of thefinal astigmatic component with completion of the resultant test;

FIG. 6 is a perspective view of an alternate embodiment using cylindersmear of point sources of light for the measurement of one component ofpatient astigmatism;

FIG. 7 is a patient's eye view of the preferred target of this inventionwhen optimum astigmatic correction has been achieved;

FIG. 8 is a view of the same target where optimum astigmaticprescription has not been achieved;

FIG. 9 is a view of the apparatus of FIG. 6 illustrating the smearingcylinder and target of this invention aligned at 45° with respect to thealignment shown in FIG. 6 for testing of the remaining component ofpatient astigmatism;

FIG. 10 is a patient's eye view of the target through the apparatusdisclosed where astigmatic prescription along the remaining component ofastigmatic acuity has been determined;

FIG. 11 is a view of the target where correct astigmatism correction hasnot been determined; and,

FIG. 12 is a graphic plot illustrating how astigmatic measurements canbe combined on the plot to prescribe rotation and power of cylindricalalignment.

Referring to FIG. 1, a schematic diagram in partial perspectiveillustrating an apparatus which can be used for the practice of theprocess of this invention is illustrated. Viewing the perspective andschematic view from left to right, a target T consisting of a straightline 14 is first illustrated. Typically, straight line 14 is a line ofone minute of arc or less to the patient's eye (this dimension being atthe maximum of visual acuity of the eye) although coarser targets mayalso be useful. The target T can be generated in any number forconventional ways, from the conventional eye chart to projectors and thelike.

The patient P, schematically illustrated at eye 15, views target Tthrough corrective optics. Responsive to his visual clarity of thetarget T being viewed, adjustment is sequentially made to the sphericaloptic lens pairs 16 (for the first time), the first astigmatic powerlens pair 18, the spherical optic lens pairs 16 (for the second time),and finally to the second astigmatic power lens pair 20.

Spherical optic lens pairs 16 are known. (See U.S. Pat. No. 3,305,294,issued Feb. 21, 1967, entitled "Two Element Variable Power SphericalLens" to Luis W. Alvarez and U.S. Pat. No. 3,507,565 issued April 21,1970, entitled "Variable Power Lens and System" to Luis W. Alvarez andWilliam E. Humphrey.)

Broadly, spherical optic lens pairs 16 are moved relatively one to theother responsive to the subjective patient manifestations of visualacuity of target T. The spherical optics move gradually and continuouslyto generate either positive spherical power or negative spherical powerby relative movement of one lens element 16 relative to the other lenselement 16.

First and second astigmatic optics 18 and 20 are known. (See U.S. Pat.No. 3,751,138, issued Aug. 7, 1973, to William E. Humphrey, entitled"Variable Anamorphic Lens and Method for Constructing Lens".)

Regarding lens pairs 16, 18 and 20, the reader should realize that theseare extremely complex optical surfaces. These extremely complex surfacesare here schematically shown as flat pieces of glass. Their complexsurfaces can only be understood after referring to the referenced U.S.Pat. Nos. 3,305,294; 3,507,565; and 3,751,138.

Broadly, first astigmatic optic lens pairs 18 are moved relatively oneto the other responsive to subjective patient manifestations of visualacuity of target T. First astigmatic lens pairs 18 change the astigmaticpower or focal length from positive to negative along one diagonal andsimultaneously change the astigmatic lens power from negative topositive along the remaining diagonal. Opposite relative horizontalmovement produces opposite astigmatic adjustments.

Likewise, second astigmatic lens pairs 20 are moved relatively one tothe other responsive to subjective patient manifestations of visualacuity of target T. Second astigmatic optics 20 change the astigmaticpower or focal length from positive to negative along the vertical axisand simultaneously from negative to positive along the horizontal axisupon relative movement of each of the lenses of the lens pairs inrelative horizontal movement. Opposite relative horizontal movementproduces opposite astigmatic adjustments.

It should be noted at this juncture that much of the mechanicalequipment which can be used to supplement the operation of thisembodiment of this invention has been disclosed elsewhere. For example,apparatus for causing equal and opposite movement to lens pairs 16, 18and 20 is described in my copending patent application Ser. No. 371,809,filed June 20, 1973, entitled "Eye Test Apparatus", now U.S. Pat. No.3,874,774.

Likewise, it will soon hereinafter be disclosed that relative movementof each of the three separate lens pairs is capable of generating opticprescriptions. Mechanism for the remote generation of both adjustedspherical optic output and astigmatic prescription output is set forthin my copending patent application Ser. NO. 263,329, filed June 15,1972, entitled "Ophthalmological Apparatus and Process HavingIndependent Astigmatic and Spherical Inputs", now U.S. Pat. No.3,822,932.

Before proceeding further with the description of this invention, oneaspect of the first embodiment illustrated in FIGS. 1-5 should be madeclear. The variable astigmatic lens element pairs 18 and 20 are of thetype that produce perpendicularly crossed positive and negativeastigmatic lens power along axes normal one to another. While the lenselements here illustrated are preferred, it is apparent that otherlenses and optic apparatus could be used for generation of this effect.For example, see my copending patent application Ser. No. 263,329, filedJune 15, 1972, entitled "Opthalmological Apparatus and Process HavingIndependent Astigmatic and Spherical Inputs", now U.S. Pat. No.3,822,932.

Having set forth the rather simple mechanics of this invention,operation of the process and apparatus for the generation of thesubjective eye test of this invention can now be understood by firstunderstanding optical limitations relating to astigmatism.

First, it will be well to emphasize why only straight line targetsconsisting of preferably a single straight line or at least a pluralityof parallel straight lines are used.

Referring to FIG. 1, it will be noted that target T is shown as a singlestraight line 14 of exaggerated width extending in the verticaldirection. An imaginary line 24, shown in broken horizontally extendinglines, is also shown. Focus of these lines relative to the imaginary andschematically shown retinal plane 26 of eye 15 of patient P will helpunderstand the function of the variable astigmatic lens pairs 18 and 20of this invention.

Assume that the eye 15 of the patient P has an appreciable astigmaticaberration. It is in the nature of astigmatism that straight lines ofcertain orientations will focus at different distances relative toretinal plane 26 of eye 15. In the view here shown, the aberration ofthe patient P causes the imaginary horizontal line 24 to focus behindthe imaginary retinal plane 26 and the vertical straight line 14 tofocus in front of the imaginary retinal plane.

Clearly, if the corrected astigmatic view is to be made of either theline targets 14 or 24, differing spherical corrections will be requiredto bring into focus and view either of the line targets 14 or 24.Understanding this, it should be doubly clear that the spoke-likemulti-lined targets of the prior art cannot be satisfactorily used withthis invention. As different lines of different angular orientation havedifferent planes of best focus in the vicinity of the retinal plane 26of a patient P having astigmatism, affording completely differentpatient viewing, only line targets having parallel lines can besatisfactorily used.

Second, once a straight line target, such as straight line target 14, isfocused to the focal length of an eye 15 having astigmatic aberration,astigmatic adjustment should be made along a plane that will not causerelative movement of the focal length of the viewed line with respect tothe retinal viewing plane of the eye. Stated in other terms, astigmatismpower adjustments should be made along normally disposed axes in equalpositive and negative powers on each respective axis, these normallydisposed axes being substantially 45° from the angle of the target.Thus, astigmatic correction in such a component can be made withoutaffecting the overall focal length of the astigmatism target.

Having these precepts explained and understood, the basic manipulativeprocess of this invention can be explained with sequential referencebeing made to FIGS. 1-5 of the drawings.

Referring to FIG. 1, patient P is asked to view line 14. Thereafter,relative movement of the spherical lens elements 16 is made responsiveto maximum or optimum visual acuity of line 14. Movement of the line tocoincidence with the retinal plane 26 of the patient P results as isillustrated in FIG. 2.

As shown in the extreme right of FIG. 2, line 14 does not appear withits full optical clarity. This is because the ambient astigmatism of thepatient P along diagonals relative to straight line 14 causes the edgesthereof to be blurred. It therefore remains to correct these astigmationaberrations without causing resultant spherically related movement ofline 14 out of the retinal plane 26.

Referring to FIG. 3, second astigmatic lens pairs 18 have been movedrelative to one another to cause optimum visual sharpness to patient P.Since second astigmatic lens pairs produce correspondent negative andpositive or positive and negative astigmatic lens power alongperpendicular axes -- each of which is diagonal to vertical straightline target 14 -- subjective improvement of the visual acuity of linetarget 14 results without any change in the focal length. Thisadjustment produces the final astigmatic prescription for one componentof astigmatism (the only qualification being that it may be desirable torepeat the entire sequence herein to optimize the optical settings).

Referring to FIG. 4, a new line target 34 has been placed for patientviewing. Preferably, this line target should be at an altered alignmentof 45° with respect to the target 14. It should be noted, however, thatprecise 45° alignment change of the target is not required. Changes intarget alignment of more than 30° can produce tolerable results.

Referring to FIG. 4, and remembering the sequence of FIGS. 1-3, it willbe remembered the astigmatic aberration of eye 15 of patient P willcause the new line target 34 to have a different focal length withrespect to the imaginary retinal focal plane 26 of eye 15. Therefore, asecond spherical correction will be made at spherical lens pairs 16.This adjustment will be made responsive to maximum patient visual acuityof new line target 34 and will cause the focal impingement of the linetarget 34 to fall on the retinal plane 26.

A surprising result occurs at this juncture of the process of thisinvention. The second adjustment of sphere to coincide straight linetarget 34 with retinal plane 26 causes the final spherical power to beknown. This occurs even though the final astigmatic component is notknown. Moreover, determination of the final astigmatic component willnot effect the final spherical setting of the illustratedinstrumentation, although transformation of the precriptions obtainedherein to the more accepted prior art prescription will result in theadjustment of sphere merely because of the presence of the changingcylinder.

It should be remembered with respect to FIG. 4, that sphericallyoptimizing the view of straight line target 34 leaves visual astigmaticclarity yet to be obtained. Stated in other words, patient P at eye 15does not get the optimum clarity of his view line 34 because of thepresence of the uncorrected astigmatic horizontal and verticalastigmatic components.

Referring to FIG. 5, first astigmatic optic lens pairs 20 are translatedone to another responsive to maximum visual acuity. The final componentof astigmatism is obtained. Again, since the respective negative andpositive or positive and negative axes of astigmatic power adjustmentare at substantial 45° alignment to straight line target 34, noresultant movement off of the retinal plane 26 can occur. Moreover, thisadjustment is the final adjustment in the process of this inventiongiving the final coordinate of the desired astigmatic prescription.

Having explained the process of this invention, it should be made clearthat the sequence of steps herein set forth can be repeated. This may bedone to optimize the prescription obtained or alternately to checkprecription accuracy.

It should also be understood that the physical positioning of lens pairs16, 18 and 20 may be permuted, if desired, without invalidating theprocedure.

It should be noted that each line target 14 of FIGS. 1-3 and 34 of FIGS.4-5 requires adjustment of only two, and never three optical components.Thus, for target 14, only spherical optics 16 and first astigmaticoptics 18 are adjusted; second astigmatic optics 20 are not adjusted.

Likewise for target 34, only spherical optics 16 and second astigmaticoptics 20 are adjusted; first astigmatic optics 18 are not adjusted.

It should also be appreciated that for each target, it does not make anydifference in what order adjustment occurs. The spherical optics can beadjusted prior to the adjustment of the applicable astigmatic optics.Conversely, the applicable astigmatic optics can be adjusted prior tothe adjustment of the spherical optics.

It is surprising to note that in the manipulation of either thespherical optics 16 or the astigmatic optics 20 for target 34, the finalprescription results. This is true whether spherical optics 16 are firstmanipulated, or astigmatic optics 20 are first manipulated.

Having set forth this first and preferred embodiment of the invention,attention can now be given to an alternate embodiment.

With reference to FIG. 6, a patient P at a patient viewing station looksalong a light path through adjustable spherical optics S, adjustablepower cylindrical optics A, constant cylinder optics C, and onto targetT. Typcially, the adjustable power cylindrical optics are varied so thatthe patient P obtains a view of the target T which is similar to thatshown in FIG. 7. By collating the power of adjustable astigmaticcorrection required to have target T appear as a patient view similar tothe view of the target shown in FIG. 7, one component of astigmatism canbe measured. The remaining component of measurement is measured by thesame device aligned as illustrated in FIG. 9. Typcially, patient P viewsrealigned target T through adjustable spherical optics S, adjustablepower astigmatic optics A', and realigned constant optic cylinder C'. Apatient view of target T with corrected astigmatic prescription alongthe remaining component is illustrated in FIG. 10.

Thereafter with respect to FIG. 12, plotting of the two measuredastigmatic inputs can be made to prescribe cylinder power and cylinderrotation.

Having generally set forth this embodiment of the invention, attentioncan now be given in some detail.

Patient P is schematically shown by an eye 44. Typically the measure ofastigmatism of the patient will relate to irregularities of thepatient's eye. Therefore, it must be understood that the patient angularalignment remains unchanged. The permanent optic cylinder and targetonly are realigned to determine a second component of astigmatism.

Adjustable spherical optics S can take any conventional form as well asthe previously described variable focus optics. Typically, Galilean typeoptics can be used.

Target T is illustrated at the far end of the optical instrument. It isshown containing three point sources 48, 49 and 50. Preferably, thesepoint sources are point sources of light, the light being provided bybackground illumination through the target T (the backgroundillumination not being shown).

Constant cylinder optics C are shown somewhat exaggerated. The cylinderoptics here are shown aligned horizontally with respect to patient P andhave a strong diopter power in the vertical direction. As illustratedherein, cylinder optics C are of approximately 12 diopters.

In actual practice the cylinder power of cylinder C can vary within widelimits. For example, cylinder power ranges within 4 and 20 diopters canbe used.

Variable astigmatic lenses A are of the type shown and described inWilliam E. Humphrey Patent Application Ser. No. 235,134 filed March 16,1972, and entitled "Variable Anamorphic Lens and Method for ConstructingLens", now U.S. Pat. No. 3,751,138, issued Aug. 7, 1973. As is set forthin great detail in tht disclosure, variable astigmatic optics can beobtained by moving specially constructed lens elements horizontally andvertically one with respect to another. Utilizing the lens configurationalignment and relative movement illustrated in FIGS. 5 and 6 of theabove entitled patent, astigmatism correction at 45° with respect to thehorizontal axis of cylinder C can be obtained.

It should be understood that variable astigmatic lenses A are here shownschematically as flat circular disc of glass. Only by reference to theabove referenced U.S. Pat. No. 3,751,138 can the extremely complexsurface of these lenses be fully understood.

It should also be understood that virtually any apparatus designed forproducing variable power astigmatic correction will work with thisinvention. For example, the counter-rotating negative and positivecylindrical lenses described and set forth in patent application Ser.No. 263,329, filed June 15, 1972, filed by William E. Humphrey, andentitled "Ophthalmological Apparatus and Process Having IndependentAstigmatic and Spherical Inupts", now U.S. Pat. No. 3,822,932 can beused. It is only required that the variable astigmatism be produced atan angle oblique to the axis of cylinder C. It is preferred that theastigmatism produced by the variable astigmatic lens elements A be at45° with respect to cylinder C.

Having set forth the simple construction of this apparatus, itsoperation can now be explained.

With the instrument orientation as shown in FIG. 6, patient P viewstarget T through strong cylindrical optic C. Cylinder C will blur therespective point sources 48-50 of target T into a series of respectivestraight lines 58-60 (see FIG. 2). First spherical correction is made tothe eyes of patient P to secure optimum view of the borders of lines 58,59 and 60. This spherical adjustment brings the lines into coincidencewith the retinal plane, as in the manner previously illustrated in FIG.2. Remembering that the point sources are disposed at the imaginaryapexes of an isosceles triangle, and assuming for the purposes ofelementary description that no astigmatic prescription is required, thepoint sources will appear largely as they are illustrated with respectto FIG. 7. Specifically, point source 48 will be blurred to a line 58,point source 49 will be blurred to a line 59, and point source 50 willbe blurred to a line 60.

Changing the assumption relating to eye 44 of patient P, the operationof the device to obtain one component of astigmatic prescription can nowbe explained. Assume that the eye of patient P includes an astigmaticaberration. Moreover, this astigmatic aberration has a component at 45°relative to the axis of cylinder C of +1 diopters of power and acomponent at right angles of -1 diopter. The target T, in the absence ofany astigmatic input at variable astigmatic optics A, would appear as itdoes in FIG. 8 to patient P. Line 59' will appear close to line 60', andrelatively spatially removed from line 58'.

Variable astigmatic optics C will next be manipulated responsive topatient visual Vernier acuity of target T. Specifically, paired variableastigmatic elements A would be translated one with respect to another toproduce a 2 diopter astigmatism correction at a rotational alignment 45°from the rotational alignment of cylinder C. Lines 58', 59' and 60'shown in FIG. 8 would tend to move to the position 58, 59 and 60 shownin FIG. 7 upon the achievement of correct astigmatic prescription. Line59 will be equidistantly spaced from lines 58 and 60.

Focusing attention on the target configurations of FIGS. 7 and 8, theVernier acuity provided by the configuration of target T can beexplained. Vernier acuity includes the ability of human beings tovisually establish alignment or centering of lines. With respect to FIG.8, it will be remembered that the combined astigmatism in the eye 44 ofpatient P at 45° to the axis of cylinder C and the power of cylinder Cincline the blurred lines 58', 59' and 60' of point sources 48, 49 and50 respectively. This inclination caused line 59' to move closer to line60'. Simultaneously, line 58' moved further away from line 59'.

It might be expected that adding astigmatism to the viewpath would blurthe lines, requiring a frequent readjustment of the sphere power tomaintain sharp lines. However, this is not the case. The addition ofastigmatism diagonal to the "smeared" lines only changes the orientationof the cylindrical smearing and not its strength or spherical component,at least to a good approximation for the angular variation usuallyinvolved.

The patient has variable power astigmatic optics A adjusted to establishequidistant spacing from the line generated by the smeared point sourcesof light 48, 49 and 50. Upon adjustment, to compensate for hisastigmatic component at 45° with respect to the axis of cylinder C, thelines from point sources of light 48, 49 and 50 will be equidistantlyspaced.

Human beings with any kind of visual acuity can normally space threelines one from another to an equidistant spacing with very high degreesof accuracy. This is herein referred to as Vernier accuity.

During the measurement of cylinder power at an angle which is 45° withrespect to the cylindrical alignment of cylinder C, it should beunderstood that the relatively strong power of cylinder C blocksastigmatism perpendicular and parallel to its alignment. While patientastigmatism in this component may cause blurred lines 58-60 to becomeslightly longer or shorter, changes in the length of these lines will besubstantially not perceptible to the patient.

It has been found that particularly with young patients having largeamounts of visual accommodation, large inputs of subconscious spherecorrection can occur. Consequently, and especially with youngerpatients, the variable spherical optics S are gradually moved to thelargest positive power for which the lines remain sharp. This causesultimate cancellation of subconscious focusing and assures reliabilityof the test.

Having set forth the measurement of astigmatism is one component, themeasurement of astigmatism the remaining component will occur with theinsrument alignment shown FIG. 9.

Regarding the instrument alignment as shown in FIG. 9, patient P remainsin the same real world alignment for view through the apparatus of FIG.9 as he does for view through the apparatus of FIG. 6. Likewise,spherical optics S illustrated in FIG. 9 remain unchanged.

Cylinder C is realigned. Typically, it is aligned to a new position C'where its axis is preferably inclined 45° with respect to the originalposition shown in FIG. 6 (although alignment changes up to 30° willagain produce tolerable results). In this position, the strong power ofcylinder C' neutralizes or overwhelms all components of astigmatismperpendicular and normal to its rotational alignment. It thus can beunderstood that the components of astigmatism originally measured arecompletely neutralized in the second test.

Target T' is similarly rotated. Point sources 48, 49 and 50 are alignedrelative to one another at a new angle 45° with respect to the alignmentof target T shown in FIG. 6. Target T' has an alignment identical to thealignment of cylinder C'. Point sources 48, 49 and 50 are all located atthe apexes of an imaginery triangle having its base parallel to therotational alignment of cylinder C'.

Variable astigmatic lenses A, it will be remembered, are of the typeshown and described in William E. Humphrey Patent Application Ser. No.235,134, filed March 16, 1972, and entitled "Variable Anamorphic Lensand Method for Constructing Lens", now U.S. Pat. No. 3,751,138 issuedAug. 7, 1973. Utilizing the lens configuration, alignment, and relativemovement illustrated in FIGS. 3 and 4 of the above entitled patent,astigmatism correction vertically and horizontally which is 45° withrespect to the axis of cylinder C can be obtained.

Just as in the previous illustration of the apparatus of FIG. 6,virtually any apparatus designed for producing variable astigmatismcorrection will work with the invention. It is only required that thevariable astigmatism be produced at an angle oblique the axis ofcylinder C. It is of course preferred that the astigmatism be producedby the variable astigmatic lens elements A' at 45° with respect to thealignment of cylinder C'.

Having realigned the instrument from the orientation shown in FIG. 6 tothe orientation shown in FIG. 9, the process of measuring the remainingcomponent of astigmatism can now be described.

As in the previous case, patient P views target T' through a strongcylinder optic C'. Cylinder C' will blur the respective point sources48-50 of target T' into a series of respective straight lines 58-60.First, spherical correction is made to secure optimum view of theborders of lines 58, 59 and 60. It will be remembered that the pointsources are disposed at imaginary apexes of an isosceles triangle.Assuming for the purposes of the elementary description that nospherical prescription is required along a horizontal or verticalcomponent located at 45° with respect to the axis of cylinder C', thepoint sources will appear largely as they are illustrated with respectto FIG. 10. Specifically, point source 48 will be blurred to a line 58,point source 49 will be blurred to a line 59, and point source 50 willbe blurred to a line 60.

Changing the assumption relating to eye 44 of the patient P, theoperation of the device to obtain the remaining component of astigmatismprescription can now be explained. Assume that the eye of the patient Pincludes an astigmatic aberration. Moreover, this astigmatic aberrationhas a horizontal component at 45° relative to the axis C of -2 dioptersof cylinder power and a vertical component of +2 diopters of cylinderpower. The target T, in the absence of any astigmatic input at variableastigmatic optics A, would appear as it does in FIG. 11 to patient P.Line 59' will appear close to line 60', and relatively spatially removedfrom line 58'.

Variable astigmatic optics A' will next be manipulated responsive topatient visual Vernier acuity of target T'. Specifically, pairedvariable astigmatic elements A' would be vertically translated one withrespect to another to produce a 4 diopter crossed cylinder (±)2 dioptersalong orthogonal axes at a rotational alignment of 45° from therotational alignment of cylinder C'. Lines 58', 49' and 60' shown inFIG. 11 would tend to move to the position 58, 59 and 60 shown in FIG.10 upon acheivement of correct astigmatic prescription. Line 59 will beequidistantly spaced from lines 58 and 60.

It should be realized that the second embodiment of the invention hereshown will admit of a number of modifications. For example a two pointsource target could be used with the smearing cylinder aligned topresent to the astigmatically corrected eye a single straight line. Theastigmatically uncorrected eye would view more than one straight line.Upon the introduction of astigmatic correction, alignment of the linesinto a single straight line would be the simple subjective visual goalfor the patient. Thus, this embodiment of the invention will admit ofthe use of any number of targets having a plurality of straight linesprovided the lines can move into a recognizable geometric alignment uponmovement of the corrective astigmatic optics.

As in the case of the previous embodiment, only two and never three ofthe optical components are manipulated for each target. Thus, for targetR, orientation of FIGS. 6-8 only, adjustment of spherical optics andhorizontal relative movement of variable astigmatic optics A and neververtical relative movement of variable astigmatic optics A is required.Likewise, for target T', orientation of FIGS. 9-11 only, adjustment ofspherical optics and vertical relative movement of variable astigmaticoptics A and never horizontal relative movement of variable astigmaticoptics A is required.

Likewise, for each orientation of target T, it should also beappreciated that it does not make any difference in what orderadjustment occurs. The spherical optics S can first be adjusted.Alternately, astigmatic optics A can first be adjusted.

Moreover, it is surprising to note that the first manipulation of eitherthe spherical optics S or the astigmatic optics A for the secondorientation of target T results in the final prescription. This is truewhether spherical optics S are first manipulated or astigmatic optics Aare first manipulated.

Having obtained the two components of astigmatism utilizing the testdevice of this invention, the use of the device to obtain the requiredprescription can now be determined. Referring to FIG. 12, the Cartesiancoordinate plot converts to conventional cylindrical lens angle.However, the cylindrical lens angle has been doubled or multiplied by afactor of 2. Thus, in the plot illustrated in FIG. 12, 180° ofcylindrical lens rotation appears over 360° of actual coordinate plot.Referring to FIG. 12, it can be seen that the compensating astigmatismsetting of the test of the apparatus aligned at FIG. 9 should be plottedas -4 diopters astigmatism along the zero degree (x) direction and thecompensating astigmatism setting of the test aligned as shown in FIG. 6should be plotted as +2 diopters astigmatism along the 45° (y)direction, resulting in an astigmatism determination requiring a totalof a 4.5 diopter cylindrical lens adjustment to the prescription at anangle of approximately 77°.

The particular lens setting used here is an extreme lens setting. Veryfew optical corrections are required that are this strong. Thisparticular illustration is given here so that the polar coordinate plotof this invention may be set forth and thereafter understood.

It will be understood that the particular form of Cartesian coordinatesused here has an additional advantage. Specifically, at low diopterpower a conventional polar coordinate system prescription of astigmaticlenses becomes unwieldly. This inconvenience is due to the margin oferror and the fact that the error increases with respect to angularrotation as lower diopter lens corrections are required.

An example of the error plotted into these coordinates can be helpful.Assume that the test apparatus of FIG. 6 and FIG. 9 has resulted each inone half of a diopter of positive cylinder correction. Assume furtherthat the uncertainty of the measurement could be ± 1/4 diopter.

Referring to FIG. 12, it can be seen that the 1/2 diopter position hasbeen plotted at 70. Moreover, the area of possible error in the 1/2diopter prescriptiion has been plotted at 72. Assuming that the visualof the patient in the astigmatic correction could fall anywhere withinthe circle 72, it can be seen that the polar coordinate plot produces alarge error in angular description. For example, assuming that the pointderived from the instrument was to fall somewhere within the circle 72,the angle of that circle could range between 11.2° and 33.7°.

The conversion of the plots to a Cartesian coordinate system not onlyhas the capability of being readily translatable into the older and moreconventional cylindrical optical description of angle of rotation anddiopter power, but can be used in a method in itself to describeastigmatic optical correction. This method, both in mathematical theoryand apparatus is set forth and claimed in Patent Application Ser. No.263,329, filed June 15, 1972, and entitled "Ophthalmological Apparatusand Process Having Independent Astigmatic and Spherical Inputs", nowWilliam E. Humphrey U.S. Pat. No. 3,822,932, and my copending PatentApplication Ser. No. 385,784, now abandoned in favor of ContinuationPatent Application Ser. No. 483,171, filed June 26, 1974, entitled"Apparatus For Ophthalmological Prescription Readout". It should beapparent to the reader that obvious alterations can be made to thisinvention. Cylindrical optics C, variable astigmatic optics A, andtarget T, as well as spherical lens S can all be changed at will,provided that the principles set forth herein are practiced.

I claim:
 1. A process for determining optometric prescription for theeye including the steps of: providing a patient viewing station;providing at least one first straight line target of first arbitrarypreselected angular alignment without regard to any suspected principalaxis of the patient's eye to a view path from said patient viewingstation; providing in said view path variable spherical optics to varythe spherical correction of said target as viewed by said patient;varying the spherical correction responsive to subjective patient visualacuity of said first straight line target; providing in said view pathfirst variable astigmatic optics for varying astigmatic lens power alongfirst intersecting diagonals at substantially equal and opposite anglesfrom the preselected angular alignment of said first straight linetarget; said first variable astigmatic optics varying said astigmaticpower from positive to negative along one axis of said firstintersecting diagonals and from negative to positive along the otheraxis of said first intersecting diagonals; and, varying the firstvariable astigmatic optic responsive to subjective patient visual acuityof said first target to obtain a first component of astigmaticprescription for each patient.
 2. A process according to claim 1 havingthe additional steps of providing at least one second straight linetarget of second preselected angular alignment, said second straightline target having an orientation of at least 30° from said firststraight line target; varying the spherical correction responsive tosubjective patient visual acuity of said second straight line target toobtain the spherical prescription for said patient.
 3. The process ofclaim 2 and including the further steps of providing in said view pathsecond variable astigmatic optics for varying astigmatic lens poweralong second intersecting diagonals at substantially equal and oppositeangles from the preselected angular alignment of said second straightline target, said second variable astigmatic optics varying saidastigmatic power from positive to negative along one intersectingdiagonal and from negative to positive along the other of saidintersecting diagonals; varing said second variable astigmatic opticsresponsive to subjective patient visual acuity to determine a secondcomponent of astigmatic prescription for said patient.
 4. A processaccording to claim 1 having the additional steps of providing at leastone second straight line target of second preselected angular alignment,said second straight line target having an orientation of at least 30°from said first straight line target; providing second variableastigmatic optics for varying astigmatic lens power along secondintersecting diagonals from the alignment of said second straight linetarget, said second variable astigmatic optics varying said astigmaticpower from positive to negative along one intersecting diagonal and fromnegative to positive along the other intersecting diagonal; and, varyingsaid second variable astigmatic optics responsive to subjective patientvisual acuity to determine a second component of astigmatic prescriptionfor said patient.
 5. A process according to claim 4 having theadditional step of varying the spherical optics responsive to subjectivepatient visual acuity of said straight line target to obtain thespherical prescription for said patient.
 6. The process of claim 1 andwherein said first variable astigmatic optics vary equally andoppositely astigmatic power along perpendicular diagonals to said firstpreselected alignment of said straight line target.
 7. The process ofclaim 1 and wherein said step of providing at least one first straightline target includes the step of providing a point source of light andsmearing said point source of light to a straight line using cylinder inthe range of 4 to 20 diopters.
 8. The process of claim 7 and wherein thestep of providing at least one first straight line target includes thestep of providing a plurality of point sources of light and smearingsaid point sources of light to parallel straight using cylinder in therange of 4 to 20 diopters.
 9. The process of claim 7 and wherein saidstep of providing a target includes a target having three point sources,each point source being located at the apexes of an isoscele trianglewith the base of said triangle being parallel to the axis of saidcylinder and wherein said varying step includes varying the power ofastigmatic optics to obtain the patient's subjective equal spacingbetween apparent lines generated by said point sources.
 10. The processof claim 7 including the further steps of realigning said cylinder inthe range of 4 to 20 diopters to a second preselected angular alignmentoblique to said original preselected angular alignment of said cylinderto obtain at least one second straight line target; realigning the axisof said first variable astigmatic optics to vary said optics obliquelywith respect to said one second straight line; and, varying the power ofsaid realigned variable cylinder optics responsive to subjective visualacuity of said patient.
 11. The process of claim 7 and wherein saidfirst variable astigmatic optics are obliquely aligned at 45° withrespect to the alignment of said cylindrical optics in the range of 4 to20 diopters.
 12. The process of claim 7 and including variable powerspherical correction between said target and said viewing station andvarying said spherical power to positive power.
 13. A process fordetermining optometric prescription for the eye including the steps of:providing a patient viewing station; providing a target having at leastone first straight line of arbitrary preselected angular alignmentwithout regard to any suspected principal axis of the patient's eye to aview path from said patient viewing station at least to said target;providing in said view path variable spherical optics to vary thespherical correction of said target as viewed to said patient; varyingsaid variable spherical optics, responsive to subjective patient visualacuity of said first straight line target; providing in said view pathfirst variable astigmatic optics for varying astigmatic lens power alongmutually intersecting diagonals at substantially equal angular intervalsfrom the alignment of said first straight line target, said firstvariable astigmatic optics varying said astigmatic power from positiveto negative along one of said diagonals and from negative to positivealong the other of said diagonals; varying the first variable astigmaticoptics responsive to subjective patient visual acuity of said firsttarget to obtain a first component of astigmatic prescription for saidpatient; providing at least one second straight line target ofpreselected angular alignment, said second straight line target having apreselected angular alignment of at least 30° from said preselectedangular alignment of said first straight line target; varying sphericalcorrection responsive to subjective patient visual acuity of said secondstraight line target to obtain the spherical prescription for saidpatient; providing in said view path second variable astigmatic lenspower along mutually intersecting diagonals at substantially equalangular intervals from the preselected alignment of said second straightline target, said second variable astigmatic optics varying saidastigmatic power from positive to negative along one of said diagonalsand from negative to positive along the other of said diagonals; and,varying said second variable astigmatic optics responsive to subjectivepatient visual acuity to determine a second component of astigmaticprescription for said patient.
 14. The process of claim 13 and whereinsaid first and second respective variable astigmatic optics varycylinder power equally and oppositely along perpendicular diagonals tosaid first and second respective straight line targets.
 15. The processof claim 13 and wherein said step of varying the first variableastigmatic optics responsive to subjective patient visual acuity of saidfirst target occurs before the step of varying the variable sphericaloptics responsive to subjective patient visual acuity of said firsttarget.
 16. The process of claim 13 and wherein said step of varying thesecond variable astigmatic optics responsive to subjective patientvisual acuity of said second target occurs before the step of varyingthe variable spherical optics responsive to subjective patient visualacuity of said second target.
 17. The process of claim 13 and whereinthe step of providing at least one straight line target includes thestep of providing a point source of light and smearing said point sourceof light to a straight line using strong cylinder in the range of 4 to20 diopters.
 18. The process of claim 13 and wherein said straight linetarget includes a plurality of parallel straight lines only. 19.Apparatus for determining optometric prescription for the eye, saidapparatus comprising: a patient viewing station; a first targetincluding at least one line of preselected and arbitrary angularalignment without regard to any suspected principal axis of saidpatient's eye; a view path from said patient viewing station to saidtarget; variable spherical optics placed in said view path for view bysaid patient; first variable astigmatic optics aligned with respect tosaid target of preselected angular alignment for varying astigmatic lenspower along intersecting diagonals at substantially equal angualrintervals from the preselected alignment of said first straight linetarget; said second variable astigmatic optics varying said astigmaticpower from positive to negative along one of said diagonals and fromnegative to positive along the other of said diagonals; a secondstraight line target of preselected angular alignment, said angularalignment of said second target having an orientation of between 30° to60° from said first straight line target; second variable astigmaticoptics in said view path between said patient viewing station and targetfor varying the astigmatic lens power along intersecting diagonals atsubstantially equal angular intervals from the alignment of said secondstraight line target; and, said second variable astigmatic opticsvarying said astigmatic power from positive to negative along one ofsaid diagonals and from negative to positive along the other of saiddiagonals.
 20. The apparatus of claim 19 and wherein said first targetincludes a plurality of straight lines of preselected angular alignment.21. The invention of claim 19 wherein said target includes at least onepoint source of light and cylinder optics in the range of 4 to 20diopters inserted in said view path between said patient viewing stationand said target to smear said point source of light into at least oneline of preselected angular alignment.
 22. An apparatus for determiningastigmatism, said apparatus comprising: a patient viewing station; atarget including a plurality of point sources; a light path between saidpatient viewing station and target; and optic cylinder of constant powerrotationally aligned to an arbitrary preselected axial rotationtransverse of said light path without regard to any suspected principalaxis of the patient's eye, said cylinder power in the range of 4 and 20diopters and said optic cylinder of constant power producing a pluralityof line targets from said plurality of point sources when said patientviews said target through said optic cylinder of constant power;variable astigmatism means placed in said light path, said variableastigmatism means having a rotational alignment oblique to the alignmentof said optic cylinder of constant power.
 23. The apparatus of claim 22and wherein said target includes a target having three point sources,each point source being located at the apex of an equilateral trianglewith the base of said equilateral triangle being parallel to the axis ofsaid permanent cylinder.